Secondary air supply system for an internal combustion engine

Abstract

An air switching valve for controlling supply of secondary air to an exhaust system of an engine closes an air release port thereof to increase an amount of secondary air to be supplied at least at an initial stage of an engine acceleration operation. The air switching valve closes a secondary air supply line to stop the supply of the secondary when the engine acceleration operation continues for more than a predetermined time period, thus to prevent an exhaust gas purifier disposed in the exhaust system from over-heat.

What is claimed is: 
     
       1. A secondary air supply system for an internal combustion engine, comprising: an air pump adapted to be driven by an engine;   a secondary air supply line extending between said air pump and the engine exhaust system;   valve means in said secondary air supply line for controlling the secondary air supply from said air pump into said engine exhaust system;   a valve actuator operatively associated with said valve means and comprising first and second air pressure chambers, a diaphragm between said air pressure chambers, a first spring member disposed in said first air pressure chamber to yieldably act on said diaphragm and restricted passage means intercommunicating said first and second air pressure chambers;   a first control pressure line through which the air pressure produced by said air pump is adapted to be supplied into said first air pressure chamber;   first controlling means in said first control pressure line for controlling the air pressure supply to said first air pressure chamber;   a second control pressure line through which the air pressure produced by said air pump is adapted to be supplied into said second air pressure chamber; and   second controlling means in said second control pressure line for controlling the air pressure supply to said second air pressure chamber;   wherein said valve means includes:   a valve housing defining therein a generally cylindrical space;   first to third partition walls disposed in said space to divide in into first to fourth chambers, said partition walls having respective first to third openings to communicate the opposed chambers with each other, said first and fourth chambers being communicated to the atmosphere, and said valve housing having air inlet and outlet respectively communicating said second and third chambers with said air pump and said engine exhaust system;   a first valve member disposed in said third chamber and operatively connected to said diaphragm of said valve actuator for movement thereby to control the communication between said second and third chambers as well as the communication between said third and fourth chambers;   a second valve member disposed in said fourth chamber and a second spring member for biasing said second valve member toward said third opening of said third partition wall to close the same when the air pressure in said third chamber is smaller than the force of said second spring; and   a third valve member disposed in said first chamber and a third spring for biasing said third valve member toward said first opening of said first partition wall to close the same when the air pressure in said second chamber is smaller than the force of said third spring, said third valve member being linked to said first valve member in such a manner that said third valve member is moved away from said first opening to open the same when the movement of said first valve member toward said second opening of said second partition wall exceeds a predetermined stroke,   said first controlling means being operative to interrupt the supply of the air pressure into said first air pressure chamber while said second controlling means being operative to supply the air pressure into said second air pressure chamber at least at the initial stage of an engine acceleration operation whereby said first valve member is driven toward said third opening to close the same to thereby supply an increased amount of secondary air to said engine exhaust system.   
     
     
       2. A second air supply system according to claim 1, wherein the spring force of said third spring is larger than that of said first spring.   
     
     
       3. A secondary air supply system according to claim 1, wherein said third valve member opens said third opening of said third partition wall when the air pressure in said second chamber exceeds the spring force of said third spring to release the air from said second chamber to the atmosphere during a time when said first valve member closes said first opening.   
     
     
       4. A secondary air supply system according to claim 1, wherein when said engine acceleration operation is continued for more than a predetermined time period, said first controlling means is operative to supply the air pressure into said first air pressure chamber while said second controlling means being operative to interrupt the supply of the air pressure into said second air pressure chamber, whereby said first valve member is driven toward said second opening to close the same, and at the same time said third valve member is moved away from said first opening to open the same so as to release all the air from said air pump into the atmosphere.   
     
     
       5. A secondary air supply system according to claim 1, wherein said first controlling means comprise a third valve housing provided with first and second ports pneumatically connected to said secondary air supply line upstream of said valve means and to said first air pressure chamber of said valve actuator, a fourth valve member disposed in said third valve housing for movement to control the communication between said first air pressure chamber and said secondary air supply line, a first vacuum-responsive valve actuator operatively associated with said fourth valve member and responsive to variation of the engine intake vacuum to actuate said fourth valve member, said first vacuum-responsive valve actuator comprising a second diaphragm cooperative with said third valve housing to define a first vacuum chamber pneumatically connected to said engine intake system and a fourth spring member operative to move said fourth valve member so that said first air pressure chamber is communicated with said secondary air supply line when the vacuum pressure in said first vacuum chamber is decreased substantially to the atmospheric pressure, and a first pressure delay valve means operative to transmit with a predetermined time delay a decrease of the engine intake vacuum to said first vacuum chamber, and   wherein said second controlling means comprise a fourth valve housing provided with third and fourth ports pneumatically connected to said secondary air supply line upstream of said valve means and to said second air pressure chamber of said valve actuator, respectively, and a fifth port pneumatically connected to the engine intake system, a fifth valve member disposed in said fourth valve housing for movement between said third and fourth ports to change-over the communication of said second air pressure chamber of said valve actuator with said secondary air supply line and with said engine intake system, a second vacuum-responsive valve actuator operatively associated with said fifth valve member and responsive to variation of the engine intake vacuum to actuate said fifth valve member, said second vacuum-responsive valve actuator comprising a third diaphragm cooperative with said fourth valve housing to define a second vacuum chamber pneumatically connected to said engine intake system and a fifth spring member operative to move said fifth valve member so that said second air pressure chamber is communicated with said engine intake system but not with said secondary air supply line when the vacuum pressure in said second vacuum chamber is decreased substantially to the atmospheric pressure, and a second pressure delay valve means operative to transmit with a predetermined time delay a decrease of the engine intake vacuum to said second vacuum chamber.